Associated Press
IWAKI, Japan — A partial meltdown was probably under way at a second nuclear reactor, a top Japanese official said today, as authorities frantically tried to prevent a similar threat from a nearby unit after a catastrophic earthquake and tsunami.
Some 170,000 people have been ordered to evacuate the area covering a radius of 12 miles around the plant in Fukushima near Iwaki. A meltdown refers to a very serious collapse of a power plant’s systems and its ability to manage temperatures. A complete meltdown would release uranium and dangerous byproducts into the environment that can pose serious health risks.
Japan dealt with the nuclear threat as it struggled to determine the scope of Friday’s twin disasters, when an 8.9-magnitude earthquake, the most powerful in the country’s recorded history, was followed by a tsunami that ravaged its northeastern coast with breathtaking speed and power.
The official count of the dead was 763, but the government said the figure could far exceed 1,000. Media reports said some 10,000 people were missing or unaccounted for.
The quake and tsunami damaged three reactors at the Fukushima Dai-ichi nuclear plant, which lost their cooling functions necessary to keep the fuel rods functioning properly. At first the Unit 1 reactor was in trouble, with an explosion destroying the walls of the room where it is placed. Later, Unit 3 also began to experience problems.
Chief Cabinet Secretary Yukio Edano said operators released slightly radioactive air from Unit 3 today, while injecting water into it to reduce pressure and temperature to save the reactor from a possible meltdown.
Still, a partial meltdown in the unit is “highly possible,” he told reporters.
“Because it’s inside the reactor, we cannot directly check it, but we are taking measures on the assumption of the possible partial meltdown,” he said.
Edano said radiation levels briefly rose above legal limits but had since declined significantly. Also, fuel rods were exposed briefly, he said, indicating that coolant water didn’t cover the rods for some time. That would further raise the temperature in the reactor vessel.
Rescue efforts boosted
The government doubled the number of troops pressed into rescue and recovery operations to about 100,000 from 51,000.
Teams searched for the missing along hundreds of miles of the Japanese coast, and thousands of hungry survivors huddled in darkened emergency centers that were cut off from rescuers and aid. At least a million households had gone without water since the quake struck. Large areas of the countryside were surrounded by water and unreachable. Some 2.5 million households were without electricity.
Powerful aftershocks continued to rock the country, including one today with a magnitude of 6.2 that originated in the sea, about 111 miles east of Tokyo.
Steps caused explosion
The explosion at the nuclear plant, Fukushima Daiichi, 170 miles northeast of Tokyo, appeared to be a consequence of steps taken to prevent a meltdown after the quake and tsunami knocked out power to the plant, crippling the system used to cool fuel rods there.
The blast destroyed the building housing the reactor, but not the reactor itself, which is enveloped by stainless steel 6 inches thick.
Inside that superheated steel vessel, water being poured over the fuel rods to cool them formed hydrogen. When officials released some of the hydrogen gas to relieve pressure inside the reactor, the hydrogen apparently reacted with oxygen, either in the air or the cooling water, and caused the explosion.
“They are working furiously to find a solution to cool the core,” said Mark Hibbs, a senior associate at the Nuclear Policy Program for the Carnegie Endowment for International Peace.
Nuclear agency officials said Japan was injecting seawater into the core — an indication, Hibbs said, of “how serious the problem is and how the Japanese had to resort to unusual and improvised solutions to cool the reactor core.”
Officials declined to say what the temperature was inside the troubled reactor, Unit 1. At 2,200 degrees Fahrenheit, the zirconium casings of the fuel rods can react with the cooling water and create hydrogen. At 4,000 F, the uranium fuel pellets inside the rods start to melt, the beginning of a meltdown.
Edano said radiation around the plant had fallen, not risen, after the blast but did not explain. Virtually any increase in dispersed radiation can raise the risk of cancer, and authorities were planning to distribute iodine, which helps protect against thyroid cancer.
Flashback to 1945
It was the first time Japan had confronted the threat of a significant spread of radiation since the greatest nightmare in its history: the 1945 atomic bombings of Hiroshima and Nagasaki by the U.S., which resulted in more than 200,000 deaths from the explosions, fallout and radiation sickness.
The Japanese utility that runs the plant said four workers suffered fractures and bruises and were being treated at a hospital. Nine residents of a town near the plant who later evacuated the area tested positive for radiation exposure, though officials said they showed no health problems.
There were grim signs that the death toll could soar. One report said no one could find four whole trains. Others said that 9,500 people in one coastal town were unaccounted for and that at least 200 bodies had washed ashore elsewhere.
AP writers Malcolm J. Foster, Mari Yamaguchi, Tomoko A. Hosaka, Shino Yuasa, Jay Alabaster, Sylvia Hui, David Nowak and Margie Mason contributed.